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Chapter 3
Troubleshooting
Network troubleshooting requires patience and logic. Generally speaking, the
cabling and workstation configurations are the likely first suspects; network
hardware is usually last on the list. The nature of the hub design dictates that it is
more likely for an entire hub to fail instead of just a single port.
Cabling Problems
Improper Cabling is the primary cause of most non-workstation problems on
Ethernet network, particularly for 100 Base-FX networks. It must be emphasized
that genuine twisted-pair cable and fiber optic cable be used to avoid many types
of cabling problems
• Wiring is definitely the problem if the Link LED does not light when the fiber
plug from a workstation is inserted into the port jack. Either correct the break
in the wire or replace the wire before proceeding
• Multi or single-mode fiber cable should match the switch's fiber transceiver.
• If a workstation (workstation A) does not work and other 100Base-X ports on
the hub are functioning, remove a fiber plug from a functioning port with a
functioning workstation (workstation B) and insert it into the suspect port. If
workstation B still works, the problem is in workstation A or in the wiring.
However, if workstation B does not work, then the hub may have a defective
port. Even if you suspect a defective port on the hub, continue testing.
Improperly wired workstations may appear to be functional, especially if they
are located near the hub. Sometimes, a port connected to an improperly wired
workstation can function marginally while another port may not work at all
• Once you have established that the hub is working properly, check all wiring
between the hub and the malfunctioning workstation. Ensure that the transmit
and receive wires have not been crossed; the two transmit wires should be
paired together as should the two receive wires
• Use a continuity checker to ensure that wires do not have breaks. By shorting
together the two wires of a pair at one end, you can use the continuity checker
at the other end. Also, check that there are no shorts between wires